There are known injection molding techniques using a mold as techniques for producing a resin molded article. As one of such injection molding techniques, a core-back injection molding is known and universally used. In the core-back injection molding, a resin containing a foaming agent (e.g., a gas or chemical foaming agent) is injected/filled in a mold and then the mold is opened by a prescribed degree, so that the resin is foamed. Specifically, according to the core-back injection molding, a core of the mold is moved such that a cavity in the mold can be expanded. Types of the core-back injection molding include: a core-back injection molding employing an operation of a platen, a core-back injection molding employing a movement of a taper-shaped pressure receiving block, a core-back injection molding employing a movement of a movable core-back plate capable of receiving a mold clamping pressure; injection pressure, and the like.
In FIG. 9, a device (i.e., a molding machine 1) intended to enhance accuracies of velocity control or stop position control in a core-back injection molding is shown. In the molding machine 1, one or two more fixed molds 4 and movable molds 3, which are of the same number as that of the fixed molds 4, are arranged to face each other, and each set of the fixed molds 4 and the movable molds 3 is clamped. Then, all of the movable molds 3 are opened from the opposing fixed molds 4 by moving them by a prescribed amount, and a pressure receiving block 8 removably mounted on each of the fixed molds 4 is removed from the respective fixed molds 4. Next, the fixed molds 4 are moved by a prescribed amount in the mold-opening direction by servomotor control or hydraulic pressure control.